Fixed bug 5362 - Mac OS ARM doesn't build Metal/Vulkan back-end/renderers

C.W. Betts

As it is, SDL2's built-in config on macOS for Metal excludes Apple Silicon. This is due to thinking that the 64-bit Mac platform would always be x86_64. My patch fixes this by using the catch-all of 64-bit platforms.

include/SDL_config_macosx.h

@@ -208,7 +208,7 @@
 #endif
 
 /* Metal only supported on 64-bit architectures with 10.11+ */
-#if TARGET_CPU_X86_64 && (MAC_OS_X_VERSION_MAX_ALLOWED >= 101100)
+#if TARGET_RT_64_BIT && (MAC_OS_X_VERSION_MAX_ALLOWED >= 101100)
 #define SDL_PLATFORM_SUPPORTS_METAL    1
 #else
 #define SDL_PLATFORM_SUPPORTS_METAL    0